Rotary piston machine



Jan. 26, 1937. E. K GI 2,068,918

ROTARY PISTON MACHINE Filed Nov. 25, 1953 Patented Jan. '26, 1937 PATENTOFFICE 2,068,918 ROTARY PISTON MACHINE Emil Kagi, Winterthur,Switzerland, assignor to the firm Sulzer Freres Socit Anonyme,Winterthur, Switzerland Application November 23, 1933, Serial No.699,366- In Switzerland July 7, 1933 3 Claims.

This invention relates to rotary piston machines such, for example, asrotary pumps or compressors and of the kind comprising a rotary pistoneccentrically arranged within a casing and carry- 5 ing a series ofblades circumferentially spaced apart on the rotor; so as to bearagainst .the interior of the casing.

Pumps and compressors of this type are liable to be noisy since a largenumber of blades are usually provided spaced apart at equal intervalsaround the circumference of the piston so that the blades, passing inrapid succession and at equal intervals over the inlet and outlet portsin the casing, produce a high pitched penetrating note. The casing ofthe machine, as also other parts, has a natural period of vibration thefrequency of which is often of substantially the same order as that ofthe note produced by the rotor. When therefore the vibrations of thecasing and those due to the rotor bladescome into resonance the note dueto the rotor is intensifled.

In a rotary piston machine according to the present invention thecircumferential distances between adjacent blades are not all equal. Inthis way the successive disturbances due to the blades do not take placeat regular intervals so that a high pitched penetrating note is notproduced, the vibrations producing a low pitch note situated within asound range scarcely perceptible by the ear.

The invention is particularly advantageous as applied to rotarycompressors wherein each cell formed between two adjacent blades isclosed during compression of the working medium and is opened when theleading blade of the pair passes over the delivery conduit or port. Thepressure in each cell, when opening commences in this manner, neveragrees exactly with the pressure in the delivery conduit. Thus, whencommunication between a cell and the delivery conduit commences eitherthe contents of the cell expand into the delivery conduit or mediumwithin the delivery conduit tends to expand into the cell. As thereforethe cells open'into the delivery conduit in succession and at regularintervals. the successive flow oscillations produce a high pitchedpenetrating note. Similarly, if the cells have not completely emptiedinto the delivery conduit so that compressed medium is carried round ineach cell from the delivery side to the suction side this medium willexpand into the suction conduit and thus cause oscillations of flow dueto this backflow, such oscillations taking place at 65 regularintervals. In accordance with the present invention the sequence of theoscillations is renderedirregular and the production of a penetratingnote thereby avoided.

Experimentshave shown that the reduction of noise is particularlypronounced when the maxi- 5 mum or minimum distance between adjacentblades differs from the mean distance by more than .05 times such meandistance.

distance between adjacent blades differ from the 20 mean suchdistance bymore than .05 times the said mean distance.

In all the constructions illustrated the medium to be delivered entersthrough an inlet conduit l, the blades 2 carried by the eccentric 25rotor or drum 3 forming cells 4 in which the medium is compressed andfinally delivered through a delivery conduit 5. Each blade 2 can slidein a slot 6 in the drum 3 so that as the drum rotates the blades areheld by centrifugal force 30 in engagement with the interior of thecasing I, the drum rotating in the direction of the arrow 5.

In the construction shown in Figure 1 the blades 2 are irregularlyspaced apart, the distance between adjacent blades uniformlydecreasing35 from a maximum at the region a to a minimum at the region I; and thenagain increasing uniformly to the maximum value at the region a.

In the construction illustrated in Figure 2 the distance betweenadjacent blades decreases and 40 increases twice. Thus, the distancebetween adjacent blades decreases uniformly from a. maximumat the regiona to a minimum at the region I), then increases uniformly to the maximumvalue at the second region a'whereupon it again 45 decreases uniformlyto the minimum value at the second region I), after which the distanceagain increases to the maximum value. In the construction shown inFigure 3 the uniform increase and decrease of the distance between ad-50 jacent blades takes place three times, i. e. a uniform decrease overeach are between the regions a. to b and a uniform increase over eachare between the regions b to a. It will be understood that if desired,and particularly for machines having drums of large diameter and a largenumber of blades, the increase and decrease of the distance betweenadjacent blades may be repeated still more often.

In the construction illustrated in Figure 4 the distance betweenadjacent blades decreases suddenly from a maximum at the region a to aminimum at the region b whereupon the distance gradually increases tothe maximum at the region a. If desired this sudden decrease and gradualincrease may be repeated several times as shown in Figure 5 in which thedistance between adjacent blades suddenly decreases from a maximum to aminimum value over each arc a to b and increases gradually from theminimum to the maximum value over each arc b to a.

Figure 6 illustrates a construction in which the distance betweenadjacent blades varies irregularly.

If the blades were regularly spaced apart, that is to say so that allthe distances between the several pairs of adjacent blades were equal,each blade in passing over the inlet and delivery conduits I and 5 wouldcause a blow-like impact so that a series of these impacts occur atregular intervals thereby producing a periodical vibration correspondingto a uniform high pitched whistling note. When, however, the blades arespaced at unequal intervals round the drum the impacts will take placeat varying intervals so that, provided the spacings of the blades havebeen suitably chosen, the individually produced vibrations willdisappear at certain points during each revolution of the drum owing tointerference and will only tend to be superposed at relatively wideintervals. The individual vibrations will be dominated by a periodicalmain vibration having a periodicity corresponding to one revolution ofthe drum and which will be perceived by the car as a fundamental noteThe remaining individual vibrations of small magnitude and superposed onthe fundamental will distort the pure fundamental, so as to produce asound in which the deep note will at all times predominate. In the case,for example, of a sixteen blade rotor embodying the invention the pitchof the note will be lower by four octaves than that of a sixteen bladerotor in which the distances between adjacent blades are equal, sincethe time of vibration is sixteen times as long and the frequency sixteentimes less.

Since the human ear perceives only sounds within a. given range ofvibration, high notes such as those produced by rotary pistons havingregularly spaced bladesare perceived as a penetrating whistling notewhilst deeper notes are perceived scarely or not at all. When the bladesare irregularly spaced the time of vibration is considerably lengthenedand the tone thus lowered so that the efl'ect on the human ear isreduced. Further, deep notes are less liable to come into resonance withparts of the machine and thus are unlikely to penetrate. the casingwalls since these-are unable to vibrate at such small frequency. Thecasing itself thus acts, in effect, as a vibration damper.

In calculating the spacing of the blades the sounds caused bycompressors of the size under consideration may be resolved in certaincircumstances into harmonic components in order blade and a radius ofthe rotor at the point where the .blade meets the rotor may differ fromthe corresponding angle of one or more of the other blades.

The invention may be applied to any rotary piston machines such, forexample, as rotary 'pumps, compressors or fans. Further, though theinvention has been described as applied to a machine in which the bladescan slide in slots formed in a drum, the invention is also applicable toother constructions such, for example, as those in which blades of thedrag type are pivotally. connected to the eccentric or rotor, so thatthe outer end of each blade is held in engagement with the inner surfaceof the casing by centrifugal force acting on the blade.

I claim:

1. A rotary piston machine comprising a casing having an inlet and anoutlet, a rotary piston eccentrically arranged within the casing, bladescarried by said rotary'piston, said blades being circumferentiallyspaced apart and movable inwardly and outwardly of said piston as itrotates, the circumferential distances between adjacent blades being notall equal, the angle between any blade and a radius of the rotor at thepoint thereon where the blade meets the circumference of the rotordiifering fromthe corresponding angle of at least one other blade.

2. A rotary piston machine comprising a casing having an inlet and anoutlet, a rotary piston eccentrically arranged within the casing, bladescarried by said rotary piston, said blades being circumferentiallyspaced apart and movable inwardly and outwardly of said piston as itrotates, the circumferential distances between adjacent blades being notall equal, the spacing of the blades taken in succession around thecircumference of the rotor in the direction of rotation graduallydecreasing from a maximum value to a minimum value and then graduallyincreasing to the maximum value.

3. A rotary piston machine comprising a casing having an inlet and anoutlet, a rotary piston eccentrically arranged within the casing, bladescarried by said rotary piston, said blades being circumferentiallyspaced apart and movable inwardly and outwardly of said piston as itrotates, the circumferential distances between adjacent blades being notall equal, the spacing of the blades taken in succession around thecircumference of the rotor in the direction of rotation graduallydecreasing from a maximum value to a minimum value and then graduallyincreasing to the maximum value, and the gradual decrease and increaseof the spacing taking place at least twice over the circumference of therotor.

EMIL KKGI.

